Method for preparing coke oven feed from coal-char blends



States METHOD FOR PREYARING COKE OVEN FEED FRQM COAL-CHAR BLENDS Robert J. Friedrich, Library, Pa., assignor to Consolidation Coal Company, a corporation of Pennsylvania This invention relates to a method for making metallurgical coke and, more specifically, to a method for blending coking coal and low temperature carbonization char obtained from a fluidized process to prepare a feed material for metallurgical coke ovens.

The present application is a continuation-in-part of my copending application 8. N. 610,644 (now abandoned), entitled Method for Preparing Coke Oven Feed From Coal-Char Blends, filed on September 18, 1956, and assigned to the assignee of the present application.

Blending of high volatile and low or medium volatile coals in preparing a coke oven feed which will produce a good metallurgical coke has long been practiced by the coking industry. High volatile coal provides the fluidity required to produce good coke but in many cases, when used alone, produces a Weak, frothy coke. Hence low and/ or medium volatile coal is blended with the high volatile coal to improve the coke quality by adding strength to the product. The low and medium volatile coals lack the fluidity necessary for good coke and, moreover, would create intolerable coke oven wall pressures if employed alone. Despite the fact that low and medium volatile coals are generally more expensive than high volatile coal, the improved coke product resulting from blending more than offsets the higher cost of the blends.

According to the ASTM classification scheme, calculated on a dry, mineral-matter-free basis, low volatile coal contains 14 to 22 percent volatile matter, medium volatile coal contains 22 to 31 percent volatile matter, and high volatile coal contains more than 31 percent volatile matter.

It has long been proposed to substitute low temperature carbonization char for blending with coking coals to prepare a feed material for by-product coke ovens. Attempts to produce metallurgical coke from blends of high volatile coal and low temperature carbonization char have not been strikingly successful. One reason for the lack of success has been the fact that blends of high volatile coal and low temperature carbonization char possess a low bulk density which greatly reduces the quantity of coke obtainable from a coke oven employing such a blend as a feed material.

In the low temperature carbonization process, a coking bituminous coal is heated to about 800 to 1200" F. for sufficient time to permit evolution of its volatile constituents in the form of gas and tar. The yield of recoverable liquid materials is from about 15 to about 40 gallons per ton of coal in contrast to a liquid yield of about 6 gallons per ton of coal resulting from the high temperature carboniza-tion which occurs in by-product coke ovens. The solid residue product of low temperature carbonization is termed char and has properties which depend upon the specific processing conditions employed for the low temperature carbonizat-ion. Where the fluidized solids contacting technique is employed in the low temperature carbonization treatment, the product char takes the form of small, flufiiy, highly porous pellets of carbonaceous material. This so-called fluidizer char has a bulk density of about 20-25 pounds per cubic foot and has a particle size distribution such that virtually all of the .fluidizer char will pass through an 8 mesh Tyler Standard screen. Normally fluidizer char contains from about 5 to 20 weight percent of volatile matter. While fluidizer char posesses many properties which render it useful for blending with coking coals to prepare a coke oven feed material, the extremely low bulk density of fluidizer char causes such blended feed material to possess a low bulk density. Consequently, a coke oven charged with such a blend can not produce the quantity ofcoke which would result from more dense blended feed material.

I have found that when both the fluidizer char and coking coal are dry, the blends do not possess this undesirable low bulk density. However, in practice, dry coal is not encountered. Coking coals are universally subjected to wet Washing treatment usually followed by transport and storage under atmospheric conditions. Thus coal which is normally available for use as a coke oven feed material possesses an equilibrium moisture content of about 6 to 8 percent by weight. Fluidizer char, on the other hand, usually will be available in a virtually dry condition since it can be blended directly upon recovery from the fluidized low temperature carbonization process.

The daily tonnage of product coke resulting from an operating coke oven increases or decreases as the bulk density of the feed is raised or lowered. The importance of maintaining the daily oven throughput at a high level is apparent when it is remembered that the fixed costs of the ovens themselves are a considerable cost item in any coking operation. The use of a coke oven feed having a high bulk density moreover offers advantages other than increased throughput in that the apparent specific gravity, stability, tumbler hardness and resistance to abrasion of the product coke are higher than that of coke produced from feeds having a lower bulk density.

I have discovered a method for blending coking coal and fluidizer char which results in an increased bulk density forthe blend, thereby eliminating the problems of decreased oven capacity previously encountered in this art. According to my invention, each ton of coking coal is first blended with from about M3 to about 1.0 gallon of a hydrocarbon oil containing at least As-gallon of aliphatic constituents and the resulting oil-treated coal is mixed with fluidizer char. Preferably the fluidizer char prior to mixing is crushed to pass through at least a 20 mesh Tyler Stand: ard screen.

Thus the principal object of my invention is to provide a process for maintaining a high coke oven throughput of good quality by increasing the density of blends of coal and fluidizer char where either or both constituents are moist prior to blending.

The addition of oil to moist coal blends for increasing the bulk density of such blends is not novel. The prior are indicates, in fact, that any oil may be added to coal blends to accomplish this purpose, so long as the boiling point is sufiiciently high to avoid rapid evaporation and the danger of creating an explosive mixture. Aromatic oils such as light water gas tar and discarded wash oil from benzol plants have .been used to increase the bulk density of wet coal. U.S. Bureau of Mines Report of Investigations 3743 (December 1943).

I have followed the teaching of the prior art by adding oils of varying classifications to existing blends of coal and fluidizer char only to discover that no appreciable increase in bulk'density occurred. The failure of the accepted methods led to the investigation which culminated in my present invention. 7

As a result of my investigations; 1 found'tha't' the final bulk density of a coal-char blend is dependent not'only upon the reagent employed, but also'uponth' sequence in which it is added to the coal and char; "No substantial increase in bullcQdensity is achieved when aromatic oils, naphthenic oils, 'or* wetting agents are employed-regardless of the blending sequence and, in fact, in some instances their use Will actually decrease the ultimate blend bulk density. Only when an aliphatic oil is added to the coal fraction prior toadmixing it with the char will the final blend bulk density approach that of coal blends currently employed as coke oven feeds.

The coal employed in the coke oven feed blends should be of good coking quality, containing less than about 8 percent moisture by weight and preferably crushed in accordance with coke oven practice. Some coke oven operators employ feed blends containing coal up to 3-inch lump in size. Coats obtained by water washing cleaning techniques normally will possess a moisture content of up to about 8 percent by weight.

The char must be one produced by fluidized low temperature carbonization of high volatile bituminous coal and preferably should be crushed to pass through about a 20 mesh Tyler Standard screen. The ratio of coal to fluidizer char for successful coke production may vary from about 4:1 to 9:1. That is, from about 80 to 90 parts of coal by weight for 20 to 1.0 parts of fluidizer char by Weight.

EXAMPLE I To illustrate my invention I prepared a blend of 85 parts by weight of coal and parts by weight fluidizer char alone. The coal was a high volatile Pittsburgh Seam coal, crushed to pass through a /s-inch screen and having about 8 percent moisture by weight. The fluidizer char, obtained by fluidized low temperature carbonization of high volatile Pittsburgh Seam coal had been crushed to pass through a 32 mesh Tyler Standard screen. ASTM bulk density of the blend was 42 pounds per cubic foot. (Standard method of test for cubic foot weight of crushed bituminous coal, ASTM D291-29, ASTM standards on coal and coke, October 1949.)

EXAMPLE II Thereafter coal from the same source as in Example I was sprayed with a high boiling fraction of straight-run Pennsylvania crude oil in an amount equivalent to A gallon per ton. A mixture of 85 parts by weight of thus oil-treated coal and 15 parts by weight of fiuidizer char from the same source as in Example I was prepared. ASTM bulk density of the blend was 50 pounds per cubic foot.

The blend prepared in Example II was then coked in a standard by-product coke oven. The resulting coke had the physical characteristics required in acceptable metallurgical coke, i.e., specific gravity, hardness, stability and resistance to abrasion.

Good metallurgical coke resulted from blends ranging from 80 parts high volatile coal and parts crushed fiuidizer char through 90 parts high volatile coal and IO'parts crushed fiuidizer char.

To emphasize the importance of utilizing the proper reagent in the proper sequence, I prepared a series of thirteen samples comprising 85 parts by weight of coal and 15 parts by weight of fluidizer char.

The coal was a high volatile Pittsburgh Seam coal having an ASTM bulk density of 47.9 pounds per cubic foot. (Standard method of test for cubic foot of crushed bituminous coal, ASTM D29l-29, ASTM standards on coal and coke, October 1949). The coal contained 5.7 weight percent of moisture and had the following size consist:

The char, obtained by fluidized low temperature carbonization of high volatile Pittsburgh Seam coal, had an ASTM bulk density of 23.1 pounds per cubic foot and contained 4.3 weight percent of moisture. The fluidizer char had the following size consist:

The ASTM bulk density of an untreated sample blend was found to be 42.6 pounds per cubic foot.

The reagents which I employed to illustrate my invention were Picco 575 oil, Picco 501 oil, Decalin and Nacconol.

Picco 575 is a selective fraction (250 C./ 395 C. cut) of coke oven tar having an initial boiling point of 250 C. It is comprised of percent aromatic constituents and 10 percent aliphatic constituents and has a mixed aniline point of 42 C. The name Picco is a registered trade name.

Picco 501 comprises an aliphatic cut of the aforementioned Picco 575. It has a distillation range of 108 C./ 338 C. and a mixed aniline point of 65 C.

Decalin is a trade name for decahydronaphthalene, a naphthenic oil having the formula C H Nacconol is the trade name of a well-known organic detergent having good wetting properties. It is an alkyl aryl sodium sulfonate.

The sequence of blending was varied as follows: 1) Each reagent was added to the coal fraction of a sample prior to blending the coal with the char; (2) each reagent was added to the char fraction of a sample prior to blending the char with the coal; and (3) each reagent was added to admixture of coal and char subsequent to blending.

The resulting bulk densities were determined according to the ASTM method and are set out in Table I.

Table I DENSI'IIES OF BLENDS IN POUNDS PER CUBIC FOOT It is apparent from the tabulated data, that the wetting agent '(Nacconol) and the naphthenic oil (Decalin) failed to produce an appreciable increase in bulk density, and in three of the six samples actually lowered the bulk density below that of the untreated blend.

The use of the essentially aromatic oil (Picco 575) resulted in a slightly more substantial increase in bulk density, which from an examination of the over-all resul-ts would appear to be attributable to the 10 percent of aliphatic constituents contained therein.

The addition of the aliphatic oil (Picco 501) to the coal prior to blending produced a remarkable increase in bulk density of the ultimate coal-char blend. The blend bulk density, it should be noted, was actually higher than that of the untreated coal. It is apparent that the sequence of blending is critical since poor-results were achieved when this same aliphatic reagent was added to the char prior to blending, or to the admixture of coal and char.

The criticality of the sequence in which the reagent is added is confirmed by the Picco 575 data. The 10 percent of aliphatic constituents contained therein produce screen. The coal had a moisture content of 7 percent by weight. The oil was a high boiling fraction of straightrun Pennsylvania crude oil. Bulk densities were determined by the ASTM method.

Table II v EFFECT OF OIL ON BgLK DENSITY OF COAL-FLUIDIZER HAIR. BLENDS Loose bulk density Quantity of oil per ton of coal (gallons) e en (pounds/cubic foot) The data of Table II clearly demonstrates that the addition of small quantities of an aliphatic oil according to the present invention increases the bulk density of the blend of coal and fluidizer char, but that the further addition of larger amounts of oil results in a decrease in the bulk density.

. In the event that a pure aliphatic oil is not available, or for any other reason it is desired to use a mixture of aliphatic constituents along with either aromatic constituents or naphthenic constituents, or both, two limitations should be kept in mind. First, at least Aa-gallon of aliphatic constituents must be blended with each ton of coal if a good coke oven feed blend is to be ultimately produced. Second, the total amount of oil added must not exceed one gallon per ton of coal treated since an excess of oil of any type will lower the bulk density. A predominantly aliphatic oil is preferred.

According to the provisions of the patent statutes, I have explained the principle, preferred construction, and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood 6 that, within the scope of the appended claims, the invention may be practiced otherwise than as specific-ally illustrated and described.

I claim:

1. The method for preparing a coke oven feed blend of suitable controlled bulk density for metallurgical coke oven use from to parts by weight of a moisture containing-high volatile coal having a moisture content of up to about 8 percent by Weight and 20 to 10 parts by Weight of low temperature carbonization char ob tained from a fluidized process which method comprises the steps, in sequence, of first blending /s to 1 gallon of a predominantly aliphatic hydrocarbon oil containing not less than As-gallon of aliphatic constituents with each ton of said coal and thereafter blending thus oil-treated coal with said char crushed to pass through a 20 mesh Tyler Standard screen, and recovering the resulting blend of increased bulk density compared with an untreated coal-char blend as a coke oven feed blend.

2. The method for preparing a coal-char blend of increased bulk density compared with the untreated coalchar blend whereby an improved coke oven feed suitable for the manufacture of metallurgical coke is obtained, which comprises the steps, in sequence, of first blending from 80 to 90 parts by Weight of high volatile coal containing about 6 to 8 percent by weight of moisture with a predominantly aliphatic hydrocarbon oil, one-eighth to one gallon of said oil, which contains not less than one-eighth gallon of aliphatic constituents, being blending per ton of said coal, and thereafter intimately blending thus oil-treated coil with from 20 to 10 parts by weight of finely divided low temperature 'carbonization char obtained from a fluidized process, and recovering the resulting blend as a coke oven feed blend of increased bulk density.

References Qited in the file of this patent UNITED STATES PATENTS 1,659,692 Kitchen Feb. 21, 1928 2,378,420 Lohr et al. June 19, 1945 2,510,158 Van Ackeren June 6, 1950 2,640,016 Martin May 26, 1953 2,787,585 Lohrey Apr. 2, 1957 OTHER REFERENCES US. Bureau of Mines, R1. 3743, December 1943, Control of Bulk Density of the Coal Charge in Byproduct Coke Ovens, 13 pages. (Pages 7-12 particularly pertinent.) 

1. THE METHOD FOR PREPARING A COKE OVEN FEED BLEND OF SUITABLE CONTROLLED BULK DENSITY FOR METALLURGICAL COKE OVEN USE FROM 80 TO 90 PARTS BY WEIGHT OF A MOISTURE CONTAINING HIGH VOLATILE COAL HAVING A MOISTURE CONTENT OF UP TO ABOUT 8 PERCENT BY WEIGHT AND 20 TO 10 PARTS BY WEIGHT OF LOW TEMPERATURE CARBONIZATION CHAR OBTAINED FROM A FLUIDIZED PROCESS WHICH METHOD COMPRISES THE STEPS, IN SEQUENCE, OF FIRST BLENDING 1/8 TO 1 GALLON OF A PREDOMINANTLY ALIPHATIC HYDROCARBON OIL CONTAINING NOT LESS THAN 1/8-GALLON OF ALIPHATIC CONSTITUENTS WITH EACH TON OF SAID COAL AND THEREAFTER BLENDING THUS OIL-TREATED COAL WITH SAID CHAR CRUSHED TO PASS THROUGH A 20 MESH TYLER STANDARD SCREEN, AND RECOVERING THE RESULTING BLEND OF INCREASED BULK DENSITY COMPARED WITH AN UNTREATED COAL-CHAR BLEND AS A COKE OVEN FEED BLEND. 